modelIntegratedPrimarySecondary

Integrated waterside economizer on the load side in a primary-secondary chilled water system

Extends from Buildings.Applications.DataCenters.ChillerCooled.Equipment.BaseClasses.PartialChillerWSE.

Information

This model implements an integrated water-side economizer (WSE) on the load side of the primary-secondary chilled water system, as shown in the following figure. In the configuration, users can model multiple chillers with only one integrated WSE.

Implementation

The WSE located on the load side can see the warmest return chilled water, and hence can maximize the hours when the WSE can operate. Also it allows the primary pumps to be shut off when the WSE can handle the entire load. This system have three operation modes: free cooling (FC) mode, partial mechanical cooling (PMC) mode and fully mechanical cooling (FMC) mode.

There are 5 valves for on/off use only, which can be controlled in order to switch among FC, PMC and FMC mode.

V1 and V2 are associated with the chiller. When the chiller is commanded to run, V1 and V2 will be open, and vice versa. Note that when the number of chillers are larger than 1, V1 and V2 are vectored models with the same dimension as the chillers.
V2 and V3 are associated with the WSE. When the WSE is commanded to run, V3 and V4 will be open, and vice versa.
V5 is for FMC only. When FMC is on, V5 is commanded to on. Otherwise, V5 is off.

The details about how to switch among different cooling modes are shown as:

For Free Cooling (FC) Mode:

V1 and V2 are closed, and V3 and V4 are open;
V5 is closed;

For Partially Mechanical Cooling (PMC) Mode:

V1 and V2 are open, and V3 and V4 are open;
V5 is closed;

For Fully Mechanical Cooling (FMC) Mode:

V1 and V2 are open, and V3 and V4 are closed;
V5 is open;

Reference

Stein, Jeff. 2009. Waterside Economizing in Data Centers: Design and Control Considerations.ASHRAE Transactions, 115(2).

Parameters

Type	Name	Default	Description
Dynamics › Pump
Modelica.Units.SI.Time	tauPump	1	Time constant of fluid volume for nominal flow in pumps, used if energy or mass balance is dynamic
Pump
Integer	numPum	numChi	Number of pumps
Modelica.Units.SI.MassFlowRate	m_flow_pum_nominal	m2_flow_chi_nominal	Nominal flow rate of the pump
Buildings.Fluid.Movers.Data.Generic[numPum]	perPum		Performance data for primary pumps
Boolean	addPowerToMedium	true	Set to false to avoid any power (=heat and flow work) being added to medium (may give simpler equations)
Real	lValPum	0.0001	Valve leakage, l=Kv(y=0)/Kv(y=1)
Modelica.Units.SI.PressureDifference	dpValPum_nominal	6000	Nominal differential pressure of the shutoff valves for primary pumps
Dynamics › Filtered flowrate
Boolean	use_riseTime	true	Set to true to continuously change motor speed
Modelica.Units.SI.Time	riseTime	30	Time needed to change motor speed between zero and full speed
Modelica.Blocks.Types.Init	initPum	initValve	Type of initialization (no init/steady state/initial state/initial output)
Real	yPum_start	fill(0, numPum)	Initial value of output from pumps:0-off, 1-on
Real	m_flow_start	fill(0, numPum)	Initial value of output from pumps
Dynamics › Time needed to open or close valve
Real	yValPum_start	fill(0, numPum)	Initial value of output:0-closed, 1-fully opened
Real	yVal5_start	0	Initial value of output from valve 5:0-closed, 1-fully opened
Shutoff valve
Real	lVal5	0.0001	Valve 5 leakage, l=Kv(y=0)/Kv(y=1)

Components

Type	Name	Description
Modelica.Blocks.Interfaces.RealInput[numPum]	yPum	Prescribed normalized flowrate for primary pumps: 1 - nominal flowrate, 0 - no flowrate
Modelica.Blocks.Interfaces.RealInput	yVal5	Actuator position for valve 5 (0: closed, 1: open)
Modelica.Blocks.Interfaces.RealOutput[numPum]	powPum	Electrical power consumed by the pumps
Buildings.Fluid.Actuators.Valves.TwoWayLinear	val5	Bypass valve: closed when fully mechanic cooling is activated; open when fully mechanic cooling is activated
Buildings.Applications.BaseClasses.Equipment.FlowMachine_m	pum	Constant speed pumps
Buildings.Fluid.Sensors.MassFlowRate	bypFlo	Bypass water mass flowrate
Fluid.FixedResistances.Junction	jun2	Junction
Fluid.FixedResistances.Junction	spl2	Splitter
Fluid.FixedResistances.Junction	jun3	Junction

Revisions

April 26, 2021, by Kathryn Hinkelman:
Added junctions and removed kFixed redundancies.
See IBPSA, #1472.
January 12, 2019, by Michael Wetter:
Removed wrong each.
December 1, 2017, by Yangyang Fu:
Changed the input connector m_flow_in into yPum to avoid multipling mass flowrate twice in the pum. This is for #1080.
July 1, 2017, by Yangyang Fu:
First implementation.